A tax is imposed on annual gross revenues of a person derived from digital advertising services in the State. For purposes of this title, the part of the annual gross revenues of a person derived from digital advertising services in the State shall be determined using an apportionment fraction: the numerator of which is the annual gross revenues of a person derived from digital advertising services in the State; and the denominator of which is the annual gross revenues of a person derived from digital advertising services in the United States. The Comptroller shall adopt regulations that determine the state from which revenues from digital advertising services are derived. A person who derives gross revenues from digital advertising services in the State may not directly pass on the cost of the tax imposed under this section to a customer who purchases the digital advertising services by means of a separate fee, surcharge, or line–item.